EarthCARE Reveals Rain as Dominant Factor in Closed-to-Open Cell Transitions in Marine Stratocumulus

Marine stratocumulus clouds play a pivotal role in Earth’s climate system, reflecting much of the incoming solar radiation back to space. One important aspect of stratocumulus clouds is their mesoscale organization, e.g. closed or open cell structures. A transition from closed to open cells usually leads to a drop in cloud albedo and consequently the clouds’ cooling effect. It is therefore important to understand when and why transitions between these cloud structures happen.

The EarthCARE satellite enables for the first time simultaneous spaceborne measurement of cloud mesoscale structure, and detailed observations below cloud top. EarthCARE’s active sensors (ATLID and CPR) can resolve the vertical profiles of marine stratocumulus, overcoming previous CloudSat limitations caused by ground clutter, and allow observations of microphysics, such as precipitation, liquid water content and droplet size. The multi-spectral imager (MSI) adds spatial context, capturing the mesoscale structure of clouds.

We use a convolutional neural network (CNN) with MSI data to identify cloud structures and analyze their microphysics using EarthCARE’s active sensors. Initial analysis shows open and closed cells have similar vertical extents and surface coupling, but open cells produce heavier and more frequent rain.

To understand the drivers for transitions from closed to open cells, we use data from the geostationary GOES-19 satellite and ERA5 wind trajectories to track the clouds measured by EarthCARE over time. This enables us to determine whether clouds observed by EarthCARE will transition to a different structure, and the timing of this transition. Combining this information with EarthCARE, we present how microphysics changes around transitions from closed to open cells. Our findings suggest that these transitions are mainly driven by rain: before transitioning, closed cells show increased rain but no significant changes in other cloud properties, like cloud top height or surface decoupling.

This study offers important insights into the cloud processes responsible for transitions between different cloud structures. A comprehensive understanding of these mechanisms is essential for assessing how the cooling effects of clouds may change in response to our changing climate.